I'd say somewhere around 3/4 throttle would be more the go on launch.

Just crank the throttle up to full power to get the feel of how much grunt flat-out has, then come back to zero and then keep increasing it until you can feel a good amount of pull - which is usually between about half and 3/4 stick.

What I try to do nowadays is keep the wings as level as possible while getting it up there pretty quickly - doesn't matter if it's ugly to start with, but if you've get some height pretty quickly you buy some time to recover. Be ready for it to drop the nose a tad and fire out towards the left. Bit of right aileron and some up-ele and you should be good to go. If you've got enough power on, you should be able to basically drop-release it with a gentle forward nudge if you're underhand launching it - if the power is up enough, it's going to want to fly anyways, so you don't need to try to javelin the thing out of your hand. Just be ready for the left roll/turn and nose-down.

Re a throttle-switch in a 6Xi, wouldn't have a clue. Just don't push the stick too high during launching and you should be ok. I find that there's not a lot of difference in engine sound on mine from just under 3/4 to full stick anyways, though it still seems to have more pull from 3/4 to 10/10 (which is a bit weird).

The 40A ESC will handle 3S no problems btw.

I was wondering where you Rx was - under the Speedie you say? Hmmm... be careful - particularly with an Orange Rx. Speedies are pretty noisy things as far as RF goes, so I hope you don't lose signal. I just jammed my ESC in the slot provided in the front bay - next to the LiPo. Check your CG, and if it's hinting tail-heavy then I'd be moving the ESC into the slot and freeing-up the Rx.

BJ